Lubricating composition

ABSTRACT

The present invention provides the use of a lubricating composition for improving anti-foaming properties, in particular as determined according to ASTM D892, wherein the lubricating composition comprises (i) a base oil comprising Fischer-Tropsch derived base oil and (ii) from 0.0001 to 10 wt % of an anti-foam agent.

FIELD OF THE INVENTION

The present invention relates to a lubricating composition, in particular to the use of said lubricating composition for providing improved anti-foaming properties such as reduced form formation and reduced stability of foam.

BACKGROUND OF THE INVENTION

Lubricating oils, including hydraulic oils, crankcase oils, driveline lubricants, greases, marine lubricants, other types of industrial lubricants, and the like, are often used to reduce friction between members and to assist in the operation of many mechanical constituents. Commonly, such lubricating oils are used in environments in which the oil is subject to mechanical agitation in the presence of air. As a consequence, air may undesirably become entrained in the oil and/or cause the formation of foam.

Foam generally refers to a collection of air bubbles formed in or on the surface of a liquid, while air entrainment generally refers to the dispersion of air bubbles within a liquid. Air entrainment and foaming in lubricating oils can be a serious concern as it may lead to problems such as inadequate lubrication, fluctuation of hydraulic pressure, poor hydraulic system performance, incomplete oil films, component wear due to reduced lubricant viscosity, and fluid deterioration due to accelerated oxidation, which may eventually lead to mechanical failure or the like. Lubricating oils therefore usually contain a defoaming agent.

In general, as a defoaming agent for lubricating oil, it is known to employ a silicone-based defoaming agent, such as polydimethylsiloxane (PDMS), fluorosilicones and silicone glycols. For instance, U.S. Pat. No. 6,251,840 discloses lubricating fluids comprising a silicone-based antifoam agent. Similarly, US20140018267 discloses a lubricating fluid comprising a combination of three polydimethylsiloxane antifoam agents. It is also known to use non-silicone anti-foam agents, such as polymethacrylate anti-foams.

While it is known to use such anti-foaming agents in lubricant compositions, it would be desirable to formulate lubricating compositions having reduced foaming tendency.

As is disclosed in for example D. J. Wedlock et al., “Gas-to-Liquids Base Oils to assist in meeting OEM requirements 2010 and beyond”, presented at the 2nd Asia-Pacific base oil Conference, Beijing, China, 23-25 October 2007, the use of Fischer-Tropsch derived base oils in lubricating compositions such as engine oils, transmission fluids, and industrial lubricants can result in various performance benefits. Examples of performance benefits by the use of Fischer-Tropsch derived base oils mentioned in the above article include: improved oxidation stability properties, improved engine cleanliness, improved wear protection, improved emissions and improved after-treatment device compatibility. Also the Fischer-Tropsch base oils allow for the formulation of low-viscosity energy conserving formulations and exhibit very good cold flow properties and high viscosity indices and low volatility.

It has been found by the present inventors that a combination of anti-foam agents and Fischer-Tropsch derived base oils can provide lubricating compositions having improved anti-foam properties.

SUMMARY OF THE INVENTION

According to the present invention there is provided the use of a lubricating composition for improving anti-foaming properties, in particular as determined according to ASTM D892, wherein the lubricating composition comprises (i) a base oil comprising a Fischer-Tropsch derived base oil and (ii) from 0.0001 to 10 wt % of an anti-foam agent.

It has surprisingly been found that the lubricating compositions herein exhibit improved anti-foaming properties.

DETAILED DESCRIPTION OF THE INVENTION

An essential feature of the lubricating compositions herein is at least one anti-foam agent.

The anti-foam agent is typically present in an amount of from 0.0001 (1 ppm) to 10 wt %, preferably from 0.0001 to 8 wt %, more preferably from 0.001 (10 ppm) to 1 wt %, even more preferably from 0.001 (10 ppm) to 0.05 wt % (500 ppm), and especially from 0.005 to 0.02 wt %, by weight of the lubricant composition.

The anti-foam agent for use herein can be a silicone anti-foam agent or a non-silicone anti-foam agent.

Suitable silicone anti-foam agents include silicone oils and silicone resins, and the like.

In one embodiment of the present invention the anti-foam agent comprises a silicone oil. The silicone oil is not generally limited and may include any silicone oil known in the art that does not adversely affect the lubricating properties of the resulting lubricating oil composition. Suitable silicone oils may include any liquid polymerized siloxane comprising one or more organic groups (“polyorganosiloxanes”). Examples of suitable silicone oils include, but are not limited to, polyalkylsiloxanes (e.g., polydimethylsiloxane), polyarylsiloxanes, polyalkoxysiloxanes, polyaryloxysiloxanes, fluorinated polysiloxanes (e.g., trifluoropropylmethylsilicone), combinations thereof, etc.

Polydimethylsiloxane is a known antifoam compound and may be produced, for example, by the hydrolysis of dimethyldihalosilane followed by condensation, or by the decomposition of dimethylcyclosiloxane followed by condensation. In certain embodiments, polydimethylsiloxane may be end blocked by the trimethylsilyl group or hydroxyl group, but is not so limited.

Generally, silicone oils suitable for use in the present invention have a kinematic viscosity at 25° C. of at least 0.5 mm/s (cSt), or in a range of from 0.5 to 1,000,000 mm²/s (cSt), or in a range of from 10,000 to 600,000 mm²/s (cSt). Silicone oil may be present in an anti-foam agent in an amount in the range of from 0.01 to more than 99 wt %, or in an amount in the range of from 1 to 10 wt %, based on the total weight of the anti-foam agent. Further, the concentration of silicone oil present in the lubricating oil composition is typically in a range of from 0.1 to 500 ppm, from 1 to 100 ppm, or from 1 to 50 ppm.

In addition to, or instead of, the silicone oil, the anti-foam agent may comprise silica particulates. Silica particulates are not generally limited and may include any type of silica particulates that are conventionally employed in anti-foam agents, provided that the silica particulates do not adversely affect the lubricating properties of the resulting lubricating oil composition. Examples of suitable silica particulates may include, but are not limited to, colloidal silica, fumed silica, precipitated silica, silica aerogel, silica xerogel, silicas having surface organosilyl groups, chemically treated silica, hydrophobic silica, etc.

Suitable silica particulates may be produced by any known method, for example, a dry method such as the thermal decomposition of a silicon halide or the reaction of a substance containing silicic acid under heat, or a wet method such as the decomposition of a metal salt of silicic acid, e.g., sodium silicate, by an acid or the aerogel method. Various grades of silica particulates are commercially available from a variety of sources in a variety of particle size distributions. Although the size of silica particulates suitable for use in the anti-foam agent is not particularly limited, the silica particulates generally may have a particle size of from about 1 nanometers (nm) to several microns. Preferably, the silica particulates may have a particle size of from about 1 to 1000 nm.

A silica aerogel is one kind of silica that may be employed. Briefly, such materials are prepared by displacing water from a silica hydrogel with a low boiling organic liquid such as ethyl alcohol, heating the treated gel in an autoclave to approximately the critical temperature of the organic liquid, and then releasing the vapors of the organic liquid from the autoclave whereby excessive shrinking or crushing of the cellular structure of the silica is avoided. The details of this technique are described in the literature and silica aerogels are commercially available.

Preferred silica particulates include “Aerosil® R208” and “Aerosil® R812” available from Evonik Industries, fumed silica available from Sigma-Aldrich Co. LLC and silica available from Chemicell GmbH.

Silica particulates may be present in the anti-foam agent in an amount in the range of from 0.01 to more than 99 wt %, or in an amount in the range of from 0.1 to 10 wt %, based on the total weight of the anti-foam agent. Further, when present, the concentration of silica particulates present in the lubricating oil composition is typically in a range of from 0.1 to 500 ppm, from 1 to 100 ppm, or from 1 to 50 ppm.

Non-silicone types of anti-foams may also be used as the anti-foam agent herein. Suitable non-silicone anti-foam agents include, for example, a polyalkyl acrylate, an alcohol ethoxy/propoxylate, a fatty acid ethoxy/propoxylate, a sorbitan partial fatty acid ester, and the like. Suitable non-silicone anti-foam agents include polymethacrylates, such as that commercially available from Cytec Industries under the trade name PC1644.

Optionally, anti-foam agents may further comprise a solvent, such as a paraffinic mineral oil, naphthenic mineral oil, petroleum naphtha, aromatics, toluene, xylene, benzene, hexane, heptane, octane, dodecane, kerosene, etc. and combinations thereof. Optionally, the silicone oil may be dispersed or dissolved in the solvent.

In certain embodiments, the lubricating oil composition can include a solvent in which the anti-foam compound(s) can be dissolved.

Examples of commercially available anti-foam agents suitable for use in the lubricating compositions herein include PC 1644 (polymethacrylate type) commercially available from Cytec Industries, Synative AC AMH-2 (a non-silicone anti-foam agent) commercially available from BASF, Xiameter PMX-200 (a silicone-based anti-foam agent) commercially available from Dow Corning and Foam Ban 149 (a silicone-based anti-foam agent) commercially available from Munzing.

The base oil used in the lubricating composition herein comprises a Fischer-Tropsch derived base oil.

Fischer-Tropsch derived base oils are known in the art. By the term “Fischer-Tropsch derived” is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the lubricating composition of the present invention include those, for example, disclosed in EP0776959, EP0668342, WO1997021788, WO2000015736, WO2000014188, WO2000014187, WO2000014183, WO2000014179, WO2000008115, WO1999041332, EP1029029, WO2001018156 and WO2001057166.

Typically, the aromatics content of a Fischer-Tropsch derived base oil, (as measured by IP-368, ASTM D2007, ASTM D7419), will be less than about 1 wt. %, alternatively less than about 0.5 wt. % or in alternate embodiments, less than about 0.1 wt. %. The base oil can have a total paraffin content of at least about 80 wt. %, alternatively at least about 85 wt. %, alternatively at least about 90 wt. %, alternatively at least about 95 wt. %, or, in certain embodiments, at least about 99 wt. %. The Fischer-Tropsch derived base oil can have a saturates content (as measured by IP-368, ASTM D2007, ASTM D7419, or any other chromatographic method that will yield similar results) of greater than about 98 wt. %, alternatively greater than about 99 wt. %, or alternatively greater than about 99.5 wt. %. The Fischer-Tropsch derived base oil can further include a maximum n-paraffin content of about 0.5 wt. % and naphthenic compound content of from 0 to less than 20 wt. %, alternatively from about 0.5 to 10 wt. %, alternatively from about 1-5 wt. %, or alternatively from about 5-10 wt. %.

Typically, the Fischer-Tropsch derived base oil or base oil blend has a kinematic viscosity at 100° C. (as measured by ASTM D 7042) in the range of from 1 to 35 mm²/s (cSt), alternatively from 1 to 25 mm²/s (cSt), alternatively from 2 to 20 mm²/s (cSt), or alternativley from 2 mm²/s to 12 mm²/s. The Fischer-Tropsch derived base oil can have a kinematic viscosity at 100° C. (as measured by ASTM D 7042) of at least 2.5 mm²/s, alternatively at least 3.0 mm²/s (e.g., “GTL 3”). In certain embodiments of the present invention, the Fischer-Tropsch derived base oil can have a kinematic viscosity at 100° C. of not greater than 5.0 mm²/s, alternatively not greater than 4.5 mm²/s, alternatively not greater than 4.2 mm²/s (e.g., “GTL 4”). In certain embodiments of the present invention, the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. of not greater than 8.5 mm²/s, alternatively not greater than 8 mm²/s (e.g., “GTL 8”). Other grades of GTL products would also be possible, based upon the specific distillation process utilized to produce the GTL product.

Further, the Fischer-Tropsch derived base oil can have a kinematic viscosity at 40° C. (as measured by ASTM D445) of from 10 to 100 mm²/s (cSt), alternatively from 15 to 50 mm²/s, alternatively from 50 to 80 mm²/s, alternatively greater than 100 mm²/s.

Also, in certain embodiments, the Fischer-Tropsch derived base oil can have a pour point (as measured according to ASTM D 5950) of less than about −10° C., alternatively less than about −20° C., alternatively less than about −30° C., alternatively less than about −40° C., and alternatively less than about −45° C.

The flash point (as measured by ASTM D92) of the Fischer-Tropsch derived base oil can be greater than 120° C., alternatively greater than 130° C., alternatively greater than 140° C.

The Fischer-Tropsch derived base oil can have a viscosity index (according to ASTM D 2270) in the range of from about 100 to 200. Alternatively, the Fischer-Tropsch derived base oil can have a viscosity index of at least 125, alternatively at least 130. In certain embodiments, the viscosity index is less than 180, alternatively less than 160, alternatively less than 150. In certain embodiments, the viscosity index can be between 125 and 180, alternatively between 130 and 160.

In the event the Fischer-Tropsch derived base oil contains a blend of two or more Fischer-Tropsch derived base oils, the above values apply to the blend of the two or more Fischer-Tropsch derived base oils.

As used herein, the term “base oil” may refer to a mixture containing more than one base oil. Suitable base oils for use in the lubricating oil composition herein in addition to the Fischer-Tropsch derived base oil include one or more of the mineral derived or synthetic base oils selected from Group I, II, III or V base oils or Group IV poly-alpha olefins (PAOs), and mixtures thereof.

By “Group I”, “Group II”, “Group III”, “Group IV” and “Group V” base oils as used herein are meant lubricating oil base oils according to the definitions of American Petroleum Institute (API) for category I, II, III, IV and V. These API categories are defined in API Publication 1509, 15th Edition, Appendix E, July 2009.

Poly-alpha olefin base oils (PAOs) and their manufacture are well known in the art. Suitable poly-alpha olefin base oils for use in the lubricating compositions herein may be derived from linear C₂ to C₃₂, preferably C₆ to C₁₆, alpha olefins. Examples of suitable feedstocks for said poly-alpha olefins can be 1-octene, 1-decene, 1-dodecene and 1-tetradecene.

In certain embodiments, the base oil as used in the lubricating composition can include a first GTL base oil, and may optionally include one or more of the oils selected from PAO, or Group I, II, III or V base oils.

Preferably, the base oil contains more than 50 wt. %, preferably more than 60 wt. %, more preferably more than 70 wt. %, even more preferably more than 80 wt. %, and most preferably more than 90 wt. % of a Fischer-Tropsch derived base oil. In an alternate embodiment, not more than 5 wt. %, alternatively not more than 2 wt. %, of the base oil is not a Fischer-Tropsch derived base oil. In certain preferred embodiments, 100 wt % of the base oil is based on one or more Fischer-Tropsch derived base oils.

Preferably the base oil or base oil blend that includes the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. of between 2 and 35 cSt, alternatively between 2 and 10.5 cSt (according to ASTM D 445).

In certain embodiments, the total amount of base oil that is incorporated in the lubricating composition herein is preferably an amount in the range of from 60 to 99 wt. %, alternatively an amount in the range of from 65 to 90 wt. %, and in certain preferred embodiments, in an amount in the range of from 70 to 85 wt. %, with respect to the total weight of the lubricating composition.

Optionally, the lubricating oil compositions herein can also include a solvency booster. As used herein, the term “solvency booster” means a component which enhances the solvency of the Fischer-Tropsch derived base oil with respect to certain additives that are included in the formulation. In certain embodiments, the solvency booster is present in an amount of between about 1 and 30 wt %, alternatively in an amount of between about 2 and 20 wt %, or alternatively in an amount between about 5 and 15 wt %. Compounds suitable for use as a solvency booster can be selected from alkylated aromatic compounds, naphthenic base oils, ester base oils, and mixtures thereof.

Alkylated naphthalenes may be produced by any suitable means known in the art, from naphthalene itself or from substituted naphthalenes which may contain one or more short chain alkyl groups having up to about eight carbon atoms, for example methyl, ethyl, and propyl. Suitable alkyl-substituted naphthalenes include alphamethylnaphthalene, dimethylnaphthalene, and ethylnaphthalene. Naphthalene itself is especially suitable since the resulting mono-alkylated products have better thermal and oxidative stability than the more highly alkylated materials. Suitable alkylated naphthalene lubricant compositions are described in U.S. Pat. No. 3,812,036, and U.S. Pat. No. 5,602,086. The preparation of alkylnaphthalenes is further disclosed in U.S. Pat. No. 4,714.794.

The alkylated aromatic compound for use herein can be selected from alkylbenzene compounds, alkylnaphthalene compounds, and mixtures thereof.

The alkylaromatic component preferably has a kinematic viscosity at 100° C. in the range of from 3 to 12 mm²/s, more preferably in the range of from 3.8 to 7 mm²/s. The viscosity index of the alkylaromatic component is above 40, preferably at or above 70.

An exemplary alkylated aromatic compound for use herein is an alkylnaphthalene compound. Examples of commercially available alkylnaphthalene compounds are those under the tradename NA-Lube (King Industries), such as NA-Lube KR 008, NA-Lube KR019, and the like, and those under the tradename Mobil MCP (ExxonMobil).

Examples of commercially available alkyl benzenes include those available under the tradename Fusyn-22 (Formosan), those available under the tradename Janex HAL (Janex), and those available under the tradename ZEROL (Shreive Chemical Products, Inc. (SCP)).

Suitable naphthenic base oils for use as a solvency booster herein includes naphthenic base oils having low viscosity index (VI), typically between about 40-80, and a low pour point, for example, a temperature of less than −20° C. Such base oils can be produced from feedstocks rich in naphthenes and low in wax content. There is no particular limitation on the type of mineral-derived naphthenic base oil which can be used in the base oil composition herein. Any mineral-derived naphthenic base oil which is suitable for use in a lubricating oil composition can be used herein. Naphthenic base oils are defined as Group V base oils according to API. Such mineral-derived base oils can be obtained by refinery processes starting from naphthenic crude feeds. Mineral-derived naphthenic base oils for use herein preferably have a pour point of below −20° C. and a viscosity index of less than 70. Such base oils can be produced from feedstocks rich in naphthenes and low in wax content. Mineral-derived naphthenic base oils are well known and described in more detail in “Lubricant base oil and wax processing”, Avilino Sequeira, Jr., Marcel Dekker, Inc, New York, 1994, ISBN 0-8247-9256-4, pages 28-35. Methods of manufacture of naphthenic base oils can be found in “Lubricants and Lubrication (Second, Completely Revised and Extended Edition)”, published by Wiley-VCH Verlag GmbH & Co. KgaA, Chapter 4, pages 46-48.

An example of a suitable naphthenic base oil for use as a solvency booster herein is that commercially available under the tradename KN4006 (China National Petroleum Corporation). Other examples of suitable naphthenic base oils for use as a solvency booster herein include those available under the tradenames Hydrocal, Hydrosol and HR Tufflo (Calumet Specialty Products), and those commercially available under the tradename Nynas (Nynas Oil Company).

Suitable esters for use as a solvency booster herein include natural and synthetic esters such as diesters and polyol esters. An example of a suitable ester for use as a solvency booster herein is the saturated polyol ester commercially available under the tradename Priolube 3970 (Croda International PLC). Other suitable esters for use as a solvency booster herein include those available under the tradename Radialube (Oleon), those available under the tradename Emery (from Emery) and those available under the tradename Esterex (ExxonMobil Chemical).

The lubricating oil compositions herein can include one or more detergent compounds having a TBN (total base number equivalent, as determined by ASTM D2896) of between about 0 and 400. In certain embodiments, the detergent compound can include one or more alkaline earth metal salicylate. Suitable alkaline earth metal salicylates include calcium, magnesium and barium salicylates, and mixtures thereof, preferably calcium salicylates.

The lubricating oil compositions herein preferably comprise from 0.01 wt % to 9 wt %, more preferably from 1 wt % to 6 wt %, even more preferably from 3.5 wt % to 5.5 wt %, of detergent, by weight of the lubricating oil composition.

In certain embodiments, the lubricating oil compositions herein can include one or more anti-oxidants. Suitable anti-oxidants for use herein include phenolic antioxidants and/or aminic antioxidants.

In one embodiment, said antioxidants are present in an amount in the range of from 0.1 to 5.0 wt. %, preferably in an amount in the range of from 0.3 to 3.0 wt. %, and more preferably in an amount of in the range of from 0.5 to 1.5 wt. %, based on the total weight of the lubricating oil composition.

Examples of aminic antioxidants which may be conveniently used include alkylated diphenylamines, phenyl-α-naphthylamines, phenyl-β-naphthylamines and alkylated α-naphthylamines.

Exemplary aminic antioxidants include dialkyldiphenylamines, such as p,p′-dioctyl-diphenylamine, p,p′-di-α-methylbenzyl-diphenylamine, and N-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines, such as mono-t-butyldiphenylamine and mono-octyldiphenylamine, bis(dialkylphenyl)amines, such as di-(2,4-diethylphenyl)amine and di(2-ethyl-4-nonylphenyl)amine, alkylphenyl-1-naphthylamines, such as octylphenyl-1-naphthylamine and n-t-dodecylphenyl-1-naphthylamine, 1-naphthylamine, arylnaphthylamines, such as phenyl-1-naphthylamine, phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine and N-octylphenyl-2-naphthylamine, phenylenediamines, such as N,N′-diisopropyl-p-phenylenediamine and N,N′-diphenyl-p-phenylenediamine, and phenothiazines, such as phenothiazine and 3,7-dioctylphenothiazine.

Preferred aminic antioxidants include those available under the following trade designations: “Sonoflex OD-3” (Seiko Kagaku Co.), “Irganox L-57” (Ciba Specialty Chemicals Co.) and phenothiazine (Hodogaya Kagaku Co.).

Exemplary phenolic antioxidants that may be used include C₇-C₉ branched alkyl esters of 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-benzenepropanoic acid, 2-t-butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol, 2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-4-alkylphenols such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-alkoxyphenols such as 2,6-di-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-ethoxyphenol, 3,5-di-t-butyl-4-hydroxybenzylmercaptooctylacetate, alkyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionates such as n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, n-butyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 2′-ethylhexyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,6-d-t-butyl-α-dimethylamino-p-cresol, 2,2′-methylene-bis(4-alkyl-6-t-butylphenol) such as 2,2′-methylenebis(4-methyl-6-t-butylphenol, and 2,2-methylenebis(4-ethyl-6-t-butylphenol), bisphenols such as 4,4′-butylidenebis(3-methyl-6-t-butylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 2,2-(di-p-hydroxyphenyl)propane, 2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane, 4,4′-cyclohexylidenebis(2,6-t-butylphenol), hexamethyleneglycol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], triethyleneglycolbis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], 2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 3,9-bis{1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methyl-phenyl)propionyloxy]ethyl}2,4,8,10-tetraoxaspiro[5,5]undecane, 4,4′-thiobis(3-methyl-6-t-butylphenol) and 2,2′-thiobis(4,6-di-t-butylresorcinol), polyphenols such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis-[3,3′-bis(4′-hydroxy-3′-t-butylphenyl)butyric acid]glycol ester, 2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenol and 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methylbenzyl)-4-methylphenol, and p-t-butylphenol—formaldehyde condensates and p-t-butylphenol—acetaldehyde condensates.

Phenolic antioxidants include those available under the following trade designations: “Irganox L-135” (Ciba Specialty Chemicals Co.), “Yoshinox SS” (Yoshitomi Seiyaku Co.), “Antage W-400” (Kawaguchi Kagaku Co.), “Antage W-500” (Kawaguchi Kagaku Co.), “Antage W-300” (Kawaguchi Kagaku Co.), “Irganox L-109” (Ciba Speciality Chemicals Co.), “Tominox 917” (Yoshitomi Seiyaku Co.), “Irganox L-115” (Ciba Speciality Chemicals Co.), “Sumilizer GA80” (Sumitomo Kagaku), “Antage RC” (Kawaguchi Kagaku Co.), “Irganox L-101” (Ciba Speciality Chemicals Co.), “Yoshinox 930” (Yoshitomi Seiyaku Co.).

The lubricating oil composition herein may include mixtures of one or more phenolic antioxidants with one or more aminic antioxidants.

According to the present invention, the lubricating composition preferably includes up to about 30 wt % of a viscosity modifier, based on the total weight of the lubricating composition. In one embodiment, the lubricating composition comprises from 20 wt % to 30 wt % of a viscosity modifier. In another embodiment, the lubricating composition includes up to about 20 wt % of a viscosity modifier. In an alternate embodiment, the lubricating composition includes between about 10 and 20 wt % of a viscosity modifier. In yet another embodiment, the lubricating composition includes between about 1 and 10 wt % of a viscosity modifier. In a preferred embodiment of the present invention, the lubricating composition is essentially free of viscosity modifier. In a particularly preferred embodiment of the present invention, the lubricating composition comprises 0 wt % of a viscosity modifier.

Examples of viscosity index improvers include copolymers of alpha-olefins and dicarboxylic acid esters such as those described in U.S. Pat. No. 4,931,197. Commercially available copolymers of alpha-olefins and dicarboxylic acid diesters include the Ketjenlube polymer esters available from Italmatch (and previously Akzo Nobel Chemicals). Other suitable examples of viscosity index improvers are polyisobutylenes; commercially available polyisobutylenes include the Oloa® products (Chevron Oronite).

Further examples of viscosity index improvers which may conveniently be used in the lubricating compositions herein include the styrene-butadiene stellate copolymers, styrene-isoprene stellate copolymers and the polymethacrylate copolymers and ethylene-propylene copolymers (also known as olefin copolymers) of the crystalline and non-crystalline type.

Suitable olefin copolymers include those commercially available under the trade designation “PARATONE®” (such as “PARATONE® 8921” and “PARATONE® 8941”) (Chevron Oronite Company LLC); those commercially available under the trade designation “HiTEC®” (such as “HiTEC® 5850B”) (Afton Chemical Corporation); and those commercially available under the trade designation “Lubrizol® 7067C” (The Lubrizol Corporation). Suitable polyisoprene polymers include those commercially available under the trade designation “SV200” (Infineum International Ltd.). Suitable diene-styrene copolymers include those commercially available under the trade designation “SV 260” (Infineum International Ltd).

The compositions herein may also include one or more anti-wear additives. Suitable anti-wear additives for use herein include zinc dithiophosphate compounds selected from zinc dialkyl-, diaryl- and/or alkylaryl-dithiophosphates, molybdenum-containing compounds, and ashless anti-wear additives such as substituted or unsubstituted thiophosphoric acids, and salts thereof.

Examples of ashless thiophosphates are known in the art. These compounds are metal-free organic compounds. Suitable ashless thiophosphates for use in the lubricating oil composition herein may include esters and/or salts of thiophosphoric acids, and substituted thiophosphoric acids. Preferably, the ashless thiophosphates are substituted by one or more hydrocarbyl groups which hydrocarbyl groups can optionally contain an acid, a hydroxy and/or an ester group. The hydrocarbyl moiety preferably is an alkyl group containing up to 12 carbon atoms. The hydrocarbyl-substituted thiophosphate preferably contains 2 or 3 hydrocarbyl groups, or is a mixture of thiophosphates containing 2 and 3 hydrocarbyl groups.

The ashless thiophosphates can contain any number of sulphur atoms directly linked to the phosphorus atom. Preferably, the thiophosphates are monothiophosphates and/or dithiophosphates.

Examples of ashless thiophosphates which may be conveniently used in the lubricating oil composition herein are described in EP0375324, U.S. Pat. No. 5,922,657, U.S. Pat. No. 4,333,841 and U.S. Pat. No. 5,093,016, and may be conveniently made according to the methods described therein.

Examples of commercially available ashless thiophosphates that may be conveniently used in the lubricating oil composition herein include those available under the trade designations “IRGALUBE L-63” and “IRGALUBE 353” (Ciba Specialty Chemicals) and that available under the trade designation “LZ 5125” (Lubrizol).

In certain embodiments, the lubricating composition can include one or more anti-wear additives selected from one or more zinc dithiophosphates. The or each zinc dithiophosphate may be selected from zinc dialkyl-, diaryl- or alkylaryl-dithiophosphates.

Examples of zinc dithiophosphates which are commercially available include those available under the trade designations “Lz 677A”, “Lz 1095”, “Lz 1097”, “Lz 1370”, “Lz 1371”, “Lz 1373” and “Lz 1395” (Lubrizol Corp.), those available under the trade designations “OLOA 260”, “OLOA 262”, “OLOA 267” and “OLOA 269R” (Chevron Oronite), and those available under the trade designation “HITEC 7169” and “HITEC 7197” (Afton Chemical).

In certain embodiments, the lubricating composition herein includes a phosphorus containing compound, preferably selected from the group consisting of phosphonates, phosphates, phosphites, phosphorothionates and dithiophosphates, and combinations thereof. Examples of commercially available dithiophosphates and phosphates are “IRGALUBE 63” and IRGALUBE 349”, respectively, both available from Ciba Specialty Chemicals.

The lubricating oil composition of the present invention has a kinematic viscosity at 40° C. in the range of from 2 mm²/s to 220 mm2/s, preferably in the range of from 32 mm²/s to 220 mm²/s.

In addition to the components mentioned above, the lubricating composition herein may further include one or more additional additives such as dispersants, extreme-pressure additives, friction modifiers, viscosity index improvers, pour point depressants, metal passivators, corrosion inhibitors, demulsifiers, anti-corrosion agents, seal compatibility agents and additive diluent base oils, etc.

As the person skilled in the art is familiar with the above and other additives, these are not further discussed here in detail.

Specific examples of such additives are described in for example Kirk-Othmer Encyclopedia of Chemical Technology, third edition, volume 14, pages 477-526.

The above-mentioned additives are typically present in an amount in the range of from 0.01 to 35.0 wt. %, based on the total weight of the lubricating composition, preferably in an amount in the range of from 0.05 to 25.0 wt. %, more preferably from 0.1 to 20.0 wt. %, based on the total weight of the lubricating composition.

The lubricating compositions herein may be conveniently prepared by admixing the one or more additives with the base oil(s).

The lubricant composition described herein can find a variety of uses as a lubricant, including but not limited to, passenger car engine oils, heavy duty diesel engine oils, transmission lubricants, turbine oils, air compressor lubricants, hydraulic fluids, gear oils, greases, transformer oils, marine lubricants, and the like.

According to another aspect of the present invention there is provided a method of improving anti-foaming properties of a lubricating composition, in particular as determined according to ASTM D892, wherein the method comprises providing a lubricating composition which comprises a Fischer-Tropsch derived base oil and from 0.0001 to 10 wt % of an anti-foam agent.

Also provided herein is a method for lubricating an internal combustion engine, the method comprising the step of lubricating said engine with the lubricating compositions described hereinabove.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES Lubricating Oil Compositions

Various combinations of additives and base oils were formulated. Table 1 shows the properties of the base oils.

“Base oil 1” (or “BO1” or “GTL 4”) was a Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. (ASTM D445) of approximately 3.89 cSt (mm²s⁻¹). Base oil 1 may be conveniently manufactured by the process described in e.g. WO2002070631, the teaching of which is hereby incorporated by reference.

“Base oil 2” (or “BO2”) was a commercially available Group III base oil having a kinematic viscosity at 100° C. (ASTM D445) of approximately 4.3 cSt. Base oil 2 is commercially available from e.g. SK Energy (Ulsan, South Korea) under the trade designation Yubase 4.

TABLE 1 Base Oil 1 Base Oil 2 (GTL 4) (Yubase 4) Kinematic viscosity at 18.11 19.50 40° C.¹ [cSt] Kinematic viscosity at 4.083 4.260 100° C.¹ [cSt] VI Index² 128 126 Pour point³ [° C.] −39 −15 Noack volatility⁴ 12.3 15.4 [wt. %] Saturates⁵ [wt. %] 99.8 99.8 Tertiary Carbon, %⁶ 14.0 17.7 Secondary Carbon, %⁶ 67.3 66.0 Primary Carbon, %⁶ 17.5 15.1 Epsilon carbon content, 11.3 14.1 %⁶ n- and iso-paraffins⁷ n.d. n.d. Mono-naphthenics⁷ n.d. n.d. di- and poly- n.d. n.d. naphthenics⁷ Aromatics⁵ 0.5 0.2 Dynamic viscosity at −20° C.⁸ <900 <900 [cP] Dynamic viscosity at −25° C.⁸ <900 <900 [cP] Dynamic viscosity at −30° C.⁸ 990 1460 [cP] Dynamic viscosity at −35° C.⁸ 1820 2740 [cP] ¹According to ASTM D 445 ²According to ASTM D 2270 ³According to ASTM D 5950 ⁴According to CEC L-40-A-93/ASTM D 5800 ⁵According to IP 368 (modified) ⁶According to 13C NMR ⁷According to FIMS ⁸According to ASTM D 5293 n.d. = not determined

Anti-Foam Test

In order to measure the anti-foaming performance of the various lubricating compositions set out herein, the lubricating compositions were subjected to the ASTM D892 test. In this test method, air is flowed through 200 mL of a lubricating oil sample for five minutes each at three oil temperatures of 24° C. (Seq I), 93.5° C. (Seq II), and 24° C. (Seq III) and the volume of foam formed after flowing air as well as after 10 minutes of settling time are measured. Results from ASTM D892 are reported as (mL foam after 5 minute blowing period)/(mL foam after 10 minute setting period). Improved anti-foam benefits are evidenced by a lower volume of foam (in mL).

Examples 1-8 and Comparative Examples 1-8

Table 2 below shows the formulations of Examples 1-8 and Comparative Examples 1-8 and the results when these formulations were subjected to the anti-foam test ATSM D892. In Table 2, PC 1644, Synative AC AMH-2, Xiameter PMX-200 and Foam Ban 149 are all anti-foam agents. PC 1644 is commercially available from Cytec Industries. Synative AC AMH-2 is commercially available from BASF. Xiameter PMX-200 is commercially available from Dow Corning. Foam Ban 149 is commercially available from Munzing.

TABLE 2 Comparative Comparative Comparative Comparative Example Example Example 1 Example 2 Example Example Example 3 Example 4 Component 1 (wt %) 2 (wt %) (wt %) (wt %) 3 (wt %) 4 (wt %) (wt %) (wt %) Base Oil 1 99.995 99.99 99.995 99.99 (GTL 4) Base Oil 2 99.995 99.99 99.995 99.99 (Yubase 4) PC 1644 0.005 0.01 0.005 0.01 Synative 0.005 0.01 0.005 0.01 AC AMH-2 Total 100 100 100 100 100 100 100 100 ASTM D892 (mL foam): Seq I 0/0 0/0 30/0 30/0 0/0 10/0  20/0 20/0 Seq II 0/0 0/0  0/0  0/0 0/0 0/0 20/0 20/0 Seq III 0/0 0/0 30/0 20/0 0/0 0/0  0/0 10/0 Comparative Comparative Comparative Comparative Example Example Example 5 Example 6 Example Example Example 7 Example 8 Component: 5 (wt %) 6 (wt %) (wt %) (wt %) 7 (wt %) 8 (wt %) (wt %) (wt %) Base Oil 1 99.995 99.99 99.995 99.99 (GTL 4) Base Oil 2 99.995 99.99 99.995 99.99 (Yubase 4) Xiameter 0.005 0.01 0.005 0.01 PMX-200 Foam Ban 0.005 0.01 0.005 0.01 149 Total 100 100 100 100 100 100 100 100 ASTM D892 (mL foam): Seq I 0/0 10/0  20/0 20/0 0/0 0/0 10/0 10/0 Seq II 0/0 0/0 20/0 20/0 0/0 0/0  0/0  0/0 Seq III 0/0 0/0  0/0 10/0 0/0 0/0 10/0 10/0

Discussion

In the foaming test ASTM D892, the lower the amount of foam produced, the better the anti-foam properties of the composition. From Table 2 it can be seen that there is a tendency for Comparative Examples 1-8 (containing Yubase 4) to produce higher amounts of foam than Examples 1-8 (containing GTL 4). 

I claim:
 1. Use of a lubricating composition for improving anti-foaming properties, in particular as determined according to ASTM D892, wherein the lubricating composition comprises (i) a base oil comprising a Fischer-Tropsch derived base oil and (ii) from 0.0001 to 10 wt % of an anti-foam agent.
 2. Use according to claim 1 wherein the anti-foam agent is selected from silicone anti-foam agents, non-silicone anti-foam agents and mixtures thereof.
 3. Use according to claim 2 wherein the silicone anti-foam agents are selected from silicone oils.
 4. Use according to claim 3 wherein the silicone oils are selected from polyalkylsiloxanes (e.g., polydimethylsiloxane), polyarylsiloxanes, polyalkoxysiloxanes, polyaryloxysiloxanes, fluorinated polysiloxanes (e.g., trifluoropropylmethylsilicone), and mixtures thereof.
 5. Use according to claim 1, wherein the anti-foam agent comprises silica particulates.
 6. Use according to claim 2 wherein the non-silicone anti-foam agents are selected from polymethacrylates.
 7. Use according to claim 1 wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. of from 1 mm²/s to 35 mm²/s.
 8. Use according to claim 1 wherein the base oil comprises more than 50 wt %, preferably more than 60 wt %, more preferably more than 70 wt %, even more preferably more than 80 wt %, most preferably more than 90 wt % of Fischer-Tropsch derived base oil.
 9. Method for improving anti-foaming properties of a lubricating composition, in particular as determined according to ASTM D892, wherein the method comprises providing a lubricating composition which comprises (i) a base oil comprising a Fischer-Tropsch derived base oil and (ii) 0.0001 to 10 wt % of an anti-foam agent.
 10. A lubricating oil composition comprising (i) a base oil comprising a Fischer-Tropsch derived base oil; and (ii) from 0.0001 to 10 wt % of an anti-foam agent. 